Extrusion of plastic onto a mandrel



April 26, 1960 H, F, FISHER i 2,933,769

EXTRUSION OF' PLASTIC ONTO A MANDREL Filed Sept. 30, 1955 INVENTOR.

2,933,769 nxrnUsroN or PLAsTrc oN'ro A MANDREL Harold F. Fisher, Nutley, NJ., assigner to Resistoiiex Corporation, Belleville, NJ., a corporation of New York r This invention relates to the extrusion of hollow plastic articles such as tubing. Q

ln the manufacture of'extruded articles of polytetraiiuorcethylene (better known by its trade name Teom which ter-m will hereinafter beus'ed) one of the methods used is sti-called paste extrusion. This process involves making a so-called paste by mixing fine Teon powder with a volatile liquid, preferably first pressing the mixture into preforrns and then extruding the preforms or otherwise extruding the paste through a die oriiice to form tubing. rthe freshly extruded product is. quite soft and must be handled with extreme care and supported until nited States Patentl 'i-i 2,933,769 Patented Apr. 26, 1960 2 by a constantly owing stream of liquid is supplied within the extruded tubing and around the mandrel from a 'point close to'the end of the mandrel which is adjacent the' extruder. This flowing liquid serves to lubricate the outside of the mandrel and tends to float the freshlytextruded tubing along its outer surface, substantially 'elirrif inating frictional drag. It also protects the inner wall of the tubing against damage from slight irregularities on the surface of the mandrel, such as scratches, dents, cor# rosion roughness and the like.

The invention will best be understood by the drawings in which: Fig. 1 is an elevation, more or less diagrammatic, of one form of apparatus suitable for practicing the 'invern tion; Fig. 2 is an enlarged detail, mostly in central verticall section, of the oriiice end of an extruder and the end of reference to the mandrel to the extruder for support; and

Fig. 3 is a central sectional elevation of a removableE self-sealing plug by which fluid connection may b e made .n to the end of a hollow mandrel.

it has been baked to evaporate the volatile components and sintered, which converts the extruded paste into a very tough, self-sustaining material. In the co-pending application of Alton S. Vanderhoof, Serial No. 492,896, now Patent No. 2,889,581, an extrusion method isdisclosed wherein` the tubing is extruded into a Apipe by which it is supported and protected. This process, however, is not applicable to the larger sizes of tubing, the sci-called. 10 size being the largest which can, as a practical matter, be extruded into a pipe.' Sizesof -10 and larger require some internal support and s0l the tub- A f of any other plastic materialwhich requires support while in a soft or delicate condition or until it vhas passed ihr gli some subsequent processing steps.

Heretofore the extrusion of Telion tubing onto a mandrel has presented a difficulty in that not more than three or four feet of tubing in its soft condition can be extruded on a mandrel in perfect condition because friction has prevented making longer lengths. only uneconomical to produce but many uses require tubing of much greater length than three or four feet, Other difliculties are that the frictional drag of the tubing as it slides over the mandrel seriously limits the maximum speed of extrusion and causes'defects and deformities in the soft materi-al.

The principal object of the present invention is to provide a method whereby plastic tubing may be extruded on mandrels as long as may convenientlybe handled and at a maximumA rate of speed. j

A more specific object is to provide an improved method of extruding Teiion tubing.

Other objects and advantages of the invention will in part appear and in part will be obvious from the following detailed description of the present preferred embodiment of the invention. n

According to the invention, means are provided where- Short lengths are not r Referring to Fig. 1, it shows the front end of an ex'- truder 10 having a nozzle 11 lwith the extruded tubing 12 iiowingv therefrom'onto a suitable rigid mandrel 14 such as metal tubing. The mandrel is preferably sup# ported at a slight inclination to the horizontal in the following manner. j

Referring to Fig. 2,1,the center die 15 in the' orifice of Vthe extruder nozzle 10 is drilled and tappedtoreceive the threaded shank 16 of a plug 16 which' has a reduced and preferably tapered end 17. The larger base of the end 17 has a'diameter corresponding to `the inside diam` eter of mandrel 14 and the'taper is provided to facilitate the positioning of the upper end of the mandrel thereon. The lower end of the mandrel is supportedon 'a bracket 1S attached to the rim of a catch basin 19 having a botl. tom outlet 20 which may communicate with a drain or fluid reservoir. I

Parallel with the mandrel 14 and beneath it is a trough, 21 extending from extruder nozzle 11 into catch basin 19. It may be supported at its upper end on a rest 22 and ,at its lower end in the wall of the catchbasin into which it discharges.

Whenmandrel 14, is in position ready to receive extruded tubing, as shown in the drawings, its lower end is connectedl to a iiuid supply line, for example -at valve 24,

preferably through a ilexible hose connection 25 carrying at one end the removable self-sealing plug shown in Fig. 3 which will now be described.

The tubular cylindrical body 28 has an enlarged end 29 providing a shoulder 30 and at the other end is threaded internally at 31 to receive the threaded nipple 32 of the hose end tting 34. Slidably mounted on body 28 is a tubular sleeve 35 having a tiange 36 against which bears the coil spring 38. After the sleeve 35 and spring 33 have been assembled on body 28 the iixed flange 39 is permanently or otherwise secured to body 28 as by brazing or by a threaded connection, as may be desired, to put spring 38 under substantial compression. It will thus be seen that spring 38 urges sleeve 35 toward shoulder 30 and between this sleeve and shoulder there is a resilient O-ring 40 which will be compressed by the action ofthe spring, as shown, expanding it radially outward.

The head 29 is sized to have a clearance t with the inside of the mandrel and by drawing back on liange 36 pressure on O-ring 30 is released and the plug may be easily and quickly inserted in the end of the mandrel after which release of the Viiiange will cause the G-ring to be compressed into contact with the inside wall of the mandrel, thus effecting a liuid-tight seal.

As maybe seen in` Fig. 2, the upper end of the mandrel 14 adjacent the end of plug' 16 is prnvided with a plurality of openings 41. It will be` evident that if valve 241s opened, liquid, suchv as .wa-ter, assumed to li il'df D'lSll'rc, HOW" 11116 tlc livn'd Of the mandrel and ont er the 'openings 41 inside ef tubing which is being extruded over the mandrel, having owed therec 'ver from. the extrusion orifice 42. The water' supply may be initiated after sufcient tubing has been extruded t cover the Vopenings 41 and extend'slignuy beyond them; U'p 'to this point' frictional resistance will not have develdped. From this 'point onine new of water inside tlie'tubingA in eiect' floatsit along the' mandrel and keeps' itout of frictional engagement therewith. VAsthe tubing OS'S'e'S along Athe 'l'del the fuid Will fl Out the end of the tubing into `trough 21 'and' be' conveyed linto f liefateh basin 19. The new of iuid'out f 'the'1ower ed f the 'tubing and into' 't'gh 21 iid theuc ifo, the catch basin 19 and through its outlet 2li) is indicated it 44.

When the mandrel 'has been nearly covered with tubing," extrusion is stopped, valve 24 is lclosed and the tubing severed just short of thupper end of the mandrel. The

f'dr'el may their be picked upV by its ends, Without touching the soft' tubing, and conveyed to a sintering oven.

By the means and process above described Teflon tubup to twenty feet or more in length may easily be extruded at whatever rate of'sped the extruder is capable of producing it. The rate of Huid ow inside the tubing huld be adjusted SC) that an adequate otihgj'ctiou is secured but pressures which would be suicient to expand the freshly extruded tubing should be avoided.

l anaemia Since the foregoing desription is given merely Vfor purposes of illustration it i's to be understood that the `1' 'r'1vention is not limited to the details thereof which ,are subject to many modilications.

What is claimed is. v u l. In the making 4of polytetrailuoroethylene tubing of ,substantial length by extrusion from paste and thereafter heating to vsintering temperature, the steps of extrudiug the tubing onto a hollow metal mandrel having substantial length, an outer diameter throughout saidlength slightly smaller thanthe inner diameter of the tubing, and one end removably suppor-ted'adjacent the extruder nozzle with the mandrel at a slight angle to the horizontal; maintaining between said mandrel and the tubing as the latter is extruded a constantly flowing stream of liquid owing from adjacent the extruder nozzle -to the unobstructed open end of the extruded tubing of a quantity suicient to prevent Vdamagging engagement between the tubing and the mandrel and to have the tendencyA to float and convey the tubing therealong; discontinuing the extrusion and said ow of liquid before the length of the tubing exceeds the length of the mandrel; severing the length of tubing on the mandrel; and sintering the tubing on the mandrel.

2. The method of overcoming frictional resistance to the extrusion of an elongated tube onto a hollow metal mandrel of smaller diameter than the tubing which comprises disposing the mandrel at a slightangle to thehorizontal, continually Iinjecting liquid into the lower end ol the mandrel to ow out of its higher end inside the tube being extruded thereon and back out the leading end of the tube in suliicient quantity'to maintain a constantly lowing stream of liquid between the Itube and the mandrel suicient to Vtend to float the tube therealong, whereby the tube moves along the mandrel substantially out of direct contact therewith.

3. The method of'extruding long lengths of polytetrauoroethylene tubing from paste which comprises, providing a hollow metal mandrel of less outer diameter than the inside diameter of the tubing, supporting the mandrel at a slight angle to the horizontal with one end in alineme'nt with the extruder to receive the tubing as it is extruded and the other end slightly lower, and maintaining a flow of liquid through the mandrel in a direction opposite to the movement of the tubing, out of the mandrel inside lthe tubing, and back in the direction of extrusion out the open end of the tubing to produce a flowing stream between the tubing and the mandrel sutlicient in volume to tend to iloat the tubing therealong and to maintain the tubing substantially out of frictional engagement with the mandrel.

4. vThe method of claim 3 wherein said liquid is water.

References Cited in the tile of this patent UNITED VsfrATEs PATENTS 592,127 Great Britain sept. 9, 

2. THE METHOD OF OVERCOMING FRICTIONAL RESISTANCE TO THE EXTRUSION OF AN ELONGATED TUBE ONTO A HOLLOW METAL MANDREL OF SMALLER DIAMETER THAN THE TUBING WHICH COMPRISES DISPOSING THE MANDREL AT A SLIGHT ANGLE TO THE HORIZONTAL, CONTINUALLY INJECTING LIQUID INTO THE LOWER END OF THE MANDREL TO FLOW OUT OF ITS HIGHER END INSIDE THE TUBE BEING EXTRUDED THEREON AND BACK OUT THE LEADING END OF THE TUBE IN SUFFICIENT QUANTITY TO MAINTAIN A CONSTANTLY FLOWING STREAM OF LIQUID BETWEEN THE TUBE AND THE MANDREL SUFFICIENT TO TEND TO FLOAT THE TUBE THEREALONG, WHEREBY THE TUBE MOVES ALONG THE MANDREL SUBSTANTIALLY OUT OF DIRECT CONTACT THEREWITH. 